Mulit-programmable trial stimulator

ABSTRACT

Disclosed are systems and methods which provide trial stimulators suited for use interoperatively and during patient trial. Trial stimulator embodiments provide a patient interface and/or clinician interface which appears and functions substantially the same as an interface of a pulse generator controller which will be used after a trial period. A compliance monitor feature may be provided to facilitate verifying the proper use of the trial stimulator during a trial period. A diagnostic feature may be provided to facilitate verifying proper operation of various aspects of a trial stimulator, such as electrode impedance analysis. Trial stimulators of embodiments provide stimulation to a plurality of tissues and/or areas of the body, such as spinal cord stimulation, deep brain stimulation, etcetera. Embodiments provide for multi-electrode stimulation and multi-stimulation programs. Embodiments are configured to provide active discharge of stimulation pulses as well as to utilize constant current sources in providing the stimulation pulses.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims benefit of priority to co-pending andcommonly assigned U.S. Provisional Patent Application Ser. No.60/568,384, entitled “MULTI-PROGRAMMABLE TRIAL STIMULATOR,” filed May 5,2004. The present application is related to commonly assigned U.S.patent application Ser. No. [04-001 US2], entitled “CLINICIAN PROGRAMMERFOR USE WITH TRIAL STIMULATOR,” filed concurrently herewith.

TECHNICAL FIELD

The present invention relates generally to electronic tissue stimulatorsand, more particularly, to electronic tissue stimulators adapted for usein stimulation trial situations.

BACKGROUND OF THE INVENTION

The use of electronic stimulation systems to control pain by nerve ormuscle stimulation has been in use for a number of years. For example,spinal cord stimulation (SCS) is a technique that has been used for painmanagement since the 1960s. SCS systems generally feature a pulsegenerator coupled to one or more percutaneous leads having a pluralityof electrodes disposed in an area in which neurostimulation is desired.

The pulse generator may be provided in various configurations, such as atotally implanted pulse generator (IPG) or a radio frequency (RF)system. A typical IPG configuration comprises a surgically implanted,internally-powered pulse generator and multi-electrode lead. A typicalRF system configuration comprises a surgically implanted, passivereceiver and a transmitter which is worn externally. In operation, thetransmitter communicates, through an RF signal, to the implantedreceiver to provide stimulation energy and control.

The leads used with any of the foregoing pulse generators may bepositioned within a patient's epidural space, typically parallel to theaxis of the spinal cord. The electrodes are used to deliver aparticularized electric field to a specific region of the spinal cord orsurrounding tissue. Applying an electric field across one or more nervebundles and/or nerve roots can produce paresthesia, or a subjectivesensation of numbness, tingling or “pins and needles,” at the affectednerves' dermatomes. This paresthesia, if properly directed and producedat the necessary levels, can “mask” certain forms of chronic pain.

Implantation of a pulse generator, whether a fully implanted IPG or a RFsystem receiver/transmitter, necessarily requires a neurostimulationpatient to undergo an implantation surgery. Additionally, routing a leadsubdermally between an implanted pulse generator and the tissue area tobe stimulated typically requires a relatively invasive procedure, suchas a tunneling procedure. However, a lead having electrodes thereonsuitable for providing neurostimulation when coupled to a pulsegenerator may be implanted through much less invasive means, such asthrough a laparoscopic needle procedure.

The focus, characteristics and intensity of the generated electric fieldare determined by the electrode configuration (i.e., the polarity, ifany, assumed by each electrode) and the electric pulse waveform(collectively “stimulation setting”). The waveform properties include,at least, a stimulation frequency, a stimulation pulse width and phaseinformation.

Accordingly, a physician, nurse, or clinician (referred to collectivelyherein as clinician) may advantageously couple a pulse generator to alead or leads in the course of performing a lead and/or generatorimplantation procedure on a patient in order to confirm proper operationof neurostimulation. For example, a clinician may couple a pulsegenerator to a lead during a lead implantation procedure to confirm theelectrodes are disposed at a proper location within the patient.Similarly, prior to implantation of a pulse generator, a clinician maycouple a pulse generator to a lead to determine the stimulation settingto implement in the implanted pulse generator in order to achieve thedesired results.

Additionally or alternatively, a patient may wish to experienceneurostimulation for a period of time, before undergoing procedures forimplanting a pulse generator and subdermally coupling a lead thereto, inorder to determine if the feeling associated with paresthesia isacceptable to the patient and that the therapy acceptably masks thepatient's pain. Accordingly, a lead or leads (perhaps “trial” leads tobe removed and subsequently replaced with “permanent” leads uponsuccessful conclusion of a trial period) may be laparoscopically orsurgically inserted, with an end distal to the electrodes left externalfor coupling to a pulse generator. With a suitable pulse generatorcoupled to the lead, the patient may experience the prescribedneurostimulation therapy for a trial period, e.g., several hours to 30days, to determine if the therapy is satisfactory before undergoingimplantation procedures.

Various forms of pulse generators have been provided in configurationsadapted for the foregoing trial uses (such pulse generators beingreferred to herein as “trial stimulators”). These trial stimulators havetypically been relatively limited in their functionality and features.For example, trial stimulators available today provide for connection toeither 4, 8, or 16 electrodes and no more.

Generally, the same trial stimulator configuration is used whether thepatient or the clinician is conducting the trial, although a patient maybe restricted from accessing certain features of the trial stimulator.For example, a micro-switch bank may be provided to allow a clinician toselect stimulation pulse widths and amplitudes, with a cover beingprovided to prevent a patient from accessing the micro-switch bankduring their trial period. Additionally or alternatively, a lockoutswitch or mechanism may be implemented to prevent a patient havingphysical access to particular control means, such as the aforementionedmicro-switch bank, from altering particular operational aspects of thetrail stimulator.

The foregoing trial stimulators do not present an interface which isequally easy to use in the various situations they are expected to beused in, e.g., interoperatively in the operating room and patient trial.For example, where features or functions are provided for ready accesswhen used interoperatively, such as to provide complex controlalternatives for establishing a precisely tailored stimulation program,the trial stimulator is typically not well suited for use by thepatient. Likewise, where relatively simple and intuitive features orfunctions are provided for simplified access during a patient trial,such as to facilitate a patient manipulating a relatively complexstimulation program to experience various stimulation parameters in ahome trial, the trial stimulator is typically not well suited for use bythe clinician.

Trial stimulators that have been provided in the past have generallydelivered constant voltage pulses to the lead electrodes. Traditionalwisdom has been that by delivering constant voltage, if an electrodeshould fail (e.g., become disconnected from the stimulator) the voltageto the system would remain unchanged, thus having no change on batterylife and presenting little risk of over stimulation because the voltageto the remaining electrodes would remain substantially unchanged.

Although providing some form of real-time variable stimulation, thetrial stimulators available today do not provide true continuousmulti-stimulation programs. By multi-stimulation programs, it is meantthat a first set of stimulation parameters (e.g., amplitude, pulsewidth, frequency, and electrodes) are implemented to provide a firstdesired therapy (e.g., relieve pain associated with a first portion ofthe body) and a second set of stimulation parameters are implemented toprovide a second therapy (e.g., relieve pain associated with a secondportion of the body). Multi-stimulation programs of prior trialstimulators have implemented each stimulation parameter set for apredetermined period of time (multiple stimulation pulses) before movingto a next stimulation parameter set. Even where a few differentstimulation program sets are used, e.g., 3, the cycle time for the trialstimulator returning to the first stimulation program set may be high.Patients have stated that such a periodic cycling of stimulatorparameter sets sometimes results the patient being able to feel thestimulation cycles as a “fluttering” which, although not particularlyunpleasant, is noticeable.

Another attempt at providing a patient with multiple stimulationprograms using a trial stimulator has been to implement dualstimulation. For example, a trial stimulator having 8 channels may beprovide a first stimulation parameter set to 4 electrodes whileproviding a second stimulation program parameter set to a different 4electrodes.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to systems and methods which providestimulators well suited for use in a plurality of situations, such asinteroperatively and during patient trial (e.g., trial stimulators).Additionally, trial stimulators of the present invention are adapted toprovide robust functionality, preferably with respect to theirprogramming as well as their operation.

Preferred embodiments of the present invention provide a trialstimulator having a user interface which is well suited for patienttrial use. For example, a trial stimulator configured according toembodiments of the present invention preferably provides an intuitiveinterface having graphical, textual, and/or aural prompting and simpleuser input. According to one embodiment, graphical displays such as mayinclude a battery life indicator, stimulation pulse amplitude and/orfrequency, etcetera is provided to aid a user in readily interpretingthe status of various aspects of a trial stimulator. Trial stimulatorembodiments preferably provide a patient interface which appears andfunctions substantially the same as a user interface of a pulsegenerator controller which will be used for controlling a pulsegenerator (implanted or otherwise) after the trial period, therebyallowing a patient to learn a single interface.

Embodiments of the present invention additionally or alternativelyprovide a trial stimulator having a user interface which is well suitedfor clinician use. For example, a trial stimulator user interfaceconfigured according to embodiments of the present invention mayfacilitate simplified use between a plurality of patients byautomatically resetting stimulation parameter sets and/or otherparameters to an initialization state (or perhaps querying a clinicianin this regard) when a clinician mode is entered.

A compliance monitor feature is preferably provided by a clinicianinterface of embodiments of the invention to facilitate a clinicianverifying the proper use of the trial stimulator during a trial period.For example, a compliance monitor may record information with respect tothe operation of a trial stimulator, including stimulation parameters,programs implemented, time and duration of operation of stimulationsets, etcetera, in order to allow a clinician to subsequently determineif a patient has used the trial stimulator according to a prescribedtherapy, to diagnose a patient's reported indications, etcetera.

A diagnostic feature is preferably provided by a clinician interface ofembodiments of the invention to facilitate a clinician verifying properoperation of various aspects of a trial stimulator. For example,diagnostic algorithms may be implemented which check system integrity.According to preferred embodiments, diagnostic algorithms provide forelectrode impedance analysis, such as for testing electrodes,determining if electrodes should be replaced when a stimulationgenerator is being replaced, determining if open or short circuits arepresent, etcetera. For example, a diagnostic algorithm of one embodimentmay step a test signal through combinations of electrodes to determineif an acceptable impedance is present with respect to each bipole pair,possibly providing a graphical display to readily show if impedances areacceptable or not. Impedance determinations according to the foregoingmay utilize constant current circuitry described below in providing asampling signal (e.g., a square wave) to electrodes for measuringimpedance.

Full clinician user interface functionality, such as may includeinitialization, programming, monitoring, status reporting, etcetera, ispreferably included within a trial stimulator of the present invention.For example, a clinician interface incorporated within a trialstimulator of an embodiment may provide an interface which appears andfunctions substantially the same as a clinician interface of a pulsegenerator controller which will be used for controlling a pulsegenerator (implanted or otherwise) after the trial period, therebyallowing a clinician to learn a single interface.

In order to facilitate the aforementioned intuitive patient interfaceand full featured and intuitive clinician interface without presenting anumber of inputs and/or outputs which, although present in a patienttrial mode, are not used by a patient, embodiments of the presentinvention implement an external clinician interface, preferably inaddition to the aforementioned internal clinician interface. Forexample, according to embodiments of the present invention, an externalplatform having appreciable input/output capability, such as a laptopcomputer or a personal digital assistant (PDA), is adapted to cooperatewith a trial stimulator to provide a clinician interface according tothe present invention. Accordingly, although a clinician may be enabledto access all features and functions through manipulation of aninterface integral with the trial stimulator, a more robust interface,perhaps using enhanced graphics, color, sound, speech recognition,etcetera, may be provided to a clinician using the aforementionedexternal platform.

The aforementioned external clinician interface platforms may be coupledto a trial stimulator of the present invention using wired (e.g.,universal serial bus (USB), Ethernet, fiber optic, etcetera) linksand/or wireless links (e.g., infrared, bluetooth, Institute ofElectrical and Electronic Engineers (IEEE) 802.11 wirelesscommunication, etcetera). Accordingly, preferred embodiments of thepresent invention provide a clinician interface which may easily bedisposed at various locations convenient to the clinician, evenlocations beyond the sterile field of an operating room.

Trial stimulators of embodiments of the present invention are adaptedfor use in providing stimulation to a plurality of tissues and/or areasof the body, such as spinal cord stimulation, deep brain stimulation,etcetera. Accordingly, a user interface provided according toembodiments of the present invention provides multi-mode patient and/orclinician interfaces adapted to present an interface specific to aparticular use. For example, although perhaps sharing a number offeatures and functions, separate patient and/or clinician interfaces forspinal cord stimulation and deep brain stimulation may be provided withrespect to a trial stimulator. Utilization of a particular mode mayprovide for different trial stimulator operating characteristics, suchas to implement smaller or larger amplitude increments when adjusting astimulation pulse amplitude parameter in the various modes of operation.

Embodiments of the present invention provide multi-channel trialstimulators. For example, an embodiment of the present inventionprovides 32 separate channels allowing control of 32 electrodes in anyof three states (positive polarity, negative polarity, and neutral).According to embodiments, the plurality of channels may be coupled toone or more leads, each having one or more electrodes. For example, asingle lead having 32 electrodes may be controlled by a trial stimulatorof embodiments of the present invention. Likewise, 2 leads having 8electrodes each and 1 lead having 16 electrodes may be controlled by atrial stimulator of embodiments of the present invention, such as toprovide neurostimulation of different parts of a patient's body. Ofcourse, all channels provided by a trial stimulator need not be coupledto a corresponding electrode, if desired. Moreover, embodiments of thepresent invention provide for simultaneously controlling leads placed indifferent tissue types, such as to stimulate spinal regions and brainareas, using a single trial stimulator.

A trial stimulator configuration of an embodiment of the presentinvention provides a lead cable extension for coupling the trialstimulator to one or more of the foregoing leads. For example, a midlineconnector may be provided with respect to a trial lead cableconfiguration to allow the trial stimulator to be disposed at variouslocations convenient to the clinician, even locations beyond the sterilefield of an operating room, while allowing a relatively short lead cableto be used during patient trial. In use, the midline connector may bedecoupled after interoperative use of a trial stimulator by a clinicianto facilitate removal of a lead extension from the trial stimulator andconnection of the trial stimulator to the trial lead, thereby avoidingexcess lengths of lead cable during subsequent patient trial.

In energizing the aforementioned plurality of electrodes, embodiments ofthe present invention provide multiple stimulation programs. Forexample, a first stimulation program may be implemented with respect toa particular time of day or when a patient is involved in a particularactivity, whereas a second stimulation program may be implemented withrespect to a different time of day or when the patient is involved inanother activity. According to a preferred embodiment, 24 differentstimulation programs may be stored in a trial stimulator, such as forselection by a user and/or automated implementation by the trialstimulator control algorithms.

According to embodiments of the invention, stimulation programs mayimplement multiple stimulation parameter sets (a set of stimulationparameters such as may specify amplitude, pulse width, frequency, andelectrodes), thereby providing multi-stimulation programs. Thestimulation parameter sets implemented by a stimulation program of apreferred embodiment trial stimulator are changeable dynamically duringoperation of the stimulation program (e.g., “on the fly”). For example,stimulation parameters such as amplitude, pulse width, frequency,polarity, and/or selection of electrodes may be changed as a stimulationprogram continues to operate to provide stimulation. Accordingly,selecting appropriate stimulation settings, even where multiplestimulation parameter sets are employed, is streamlined according toembodiments of the invention. Moreover, interaction between multiplestimulation parameter sets may be detected and compensated for moreeasily using dynamic stimulation parameter adjustment provided accordingto preferred embodiments. For example, a clinician may implement a firststimulation parameter set, leave that stimulation set running, and thenbring in another stimulation parameter set along side of it and see ifthe combination of stimulation parameter sets (e.g., multi-stimulationprogram) is better for the patient actively, rather than testing eachindividually and then trying to join them together to ask the patienthow the combination feels. Accordingly, a clinician may adjuststimulation parameter sets dynamically and interactively with thepatient to change and optimize the stimulation therapy.

In operation according to preferred embodiments, the multiplestimulation parameter sets of a multi-stimulation program areimplemented in an interleaved fashion (e.g., a first stimulationparameter set is energized for a single pulse, followed by a secondstimulation parameter set being energized for a single pulse) ratherthan energizing each stimulation parameter set for a predeterminedperiod of time (e.g., multiple stimulation pulses) before moving to anext stimulation parameter set. Of course, stimulation programs ofembodiments of the present invention may energize one or morestimulation parameter set of a multi-stimulation program for apredetermined period of time, where desired.

To facilitate operation of multi-stimulation programs, such as thoseimplemented in an interleaved or pulse-by-pulse fashion as describedabove, embodiments of the invention are configured to provide activedischarge of electrode energizing pulses. Specifically, embodiments ofthe present invention utilize active discharge techniques to reduce thetime constant of a resistor/capacitor (RC) circuit associated withdeploying neurostimulation electrodes in a human body. Because theresistance of the living tissue is typically quite large and thecapacitor used to deliver stimulation pulses of desired magnitudes whileblocking direct current (DC) are also typically relatively large, the RCtime constant can limit the frequency at which stimulation pulses may bedelivered (such as to 250 Hz) and/or result in stimulation pulse waveforms which are other than optimal (e.g., not substantially a squarepulse). Accordingly, rather than allowing a DC blocking capacitor todrain into the tissue surrounding the electrode, embodiments of thepresent invention follow a stimulation pulse by driving the circuit inthe opposite direction to actively discharge the DC blocking capacitor,thereby reducing the circuits effective time constant.

According to embodiments of the invention, active discharge of electrodeenergizing pulses may be implemented selectively. For example, activedischarge may be implemented when the frequency of energizing pulsesexceeds a threshold, such as 200 Hz as may be associated withmulti-stimulation programs. Additionally or alternatively, differentactive discharge modes may be selectively implemented. For example, afirst mode (e.g., 1 to 4 energizing pulse to discharge driving pulse)may be implemented with respect to a first frequency range, such as 200Hz to 500 Hz, and a second mode (e.g., 1 to 2 energizing pulse todischarge driving pulse) may be implemented with respect to a secondfrequency range, such as 500 Hz to 1000 Hz.

In providing active discharge according to embodiments of the invention,constant current electrode stimulation energization pulses are utilizedalong with corresponding constant currents driven in opposite direction.Moreover, constant current stimulation is utilized to provide additionalor alternative advantages according to embodiments of the invention. Forexample, using constant current electrode stimulation according toembodiments, even if the impedance associated with one or more electrodechanges over time, the stimulation therapy experienced by the patientwill remain unchanged because it is the current between the electrodes,the current density, that triggers the therapeutic nerve response.

Embodiments of the present invention which implement constant currentelectrode stimulation employ a maximum voltage override. For example, inorder to prevent accelerated battery drain and a risk of overstimulation in a situation where constant current is used to stimulate aplurality of electrodes, one of which has failed such that no current isdelivered thereby, a maximum voltage override may be relied upon toprevent excessive voltage from being delivered to the remainingelectrodes. According to embodiments, the maximum voltage override maybe set with some headroom (e.g., 10%) above the voltage expected to beexperienced when delivering the prescribed constant current tofacilitate the aforementioned changes in impedance which are likely tooccur during treatment.

Trial stimulators configured according to embodiments of the inventioninclude a broken circuit detection feature to recognize when anelectrode is not receiving a stimulation pulse. A broken circuitdetection circuit of a preferred embodiment provides an alarm or otheralert to a user to provide notification of the broken circuit and/orstops delivering stimulation pulses, such as to avoid a patient orclinician increasing pulse magnitude before realizing a lead has becomedisconnected and thereby over stimulating the patient when the lead issubsequently reconnected. The aforementioned maximum voltage override ofembodiments of the invention may be utilized in providing a brokencircuit detection feature. For example, when a maximum voltage overridethreshold for a particular channel is reached, a trial stimulatoroperating program may conclude that a circuit has been broken withrespect to that channel.

Embodiments of the present invention provide one or more holsters foruse in carrying and/or protecting a trial stimulator. According to oneembodiment, a protective holster is provided for patient use to hold thetrial stimulator and facilitate the trial stimulator being attached to apatient's article of clothing, such as through use of a clip on theholster. A protective holster is also preferably provided for clinicianuse to hold the trial stimulator and facilitate the trial stimulatorbeing coupled to an external interface platform. Each such holsterpreferably is adapted to allow access to inputs, outputs, interfaces,etcetera appropriate to use by the corresponding user (e.g., patient orclinician).

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated that the conception and specific embodimentdisclosed may be readily utilized as a basis for modifying or designingother structures for carrying out the same purposes of the presentinvention. It should also be realized that such equivalent constructionsdo not depart from the invention as set forth in the appended claims.The novel features which are believed to be characteristic of theinvention, both as to its organization and method of operation, togetherwith further objects and advantages will be better understood from thefollowing description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWING

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawing, in which:

FIG. 1 shows a trial stimulator system configured according to anembodiment of the present invention;

FIG. 2 shows additional detail with respect to a trial stimulator ofFIG. 1;

FIG. 3 shows an alternative embodiment of a lead cable assemblyaccording to an embodiment of the invention;

FIG. 4 shows a high level block diagram of a trial stimulator configuredaccording to an embodiment of the present invention;

FIG. 5A shows a graph of passive discharge provided with respect to astimulation pulse of a trial stimulator adapted according to embodimentsof the present invention; and

FIGS. 5B-5C show graphs of active discharge provided with respect tostimulation pulses of a trial stimulator adapted according toembodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Directing attention to FIG. 1, trial stimulator system 100 configuredaccording to a preferred embodiment is shown. Trial stimulator system100 is adapted to provide delivery of electronic stimulation to apatient, such as for neurostimulation, during a trial period, such as todetermine if the patient is responsive to electronic stimulationtherapy, to determine the parameters of a particular therapy to beimplemented, etcetera. Accordingly, trial stimulator system 100 (orportions thereof) is preferably adapted for use in a plurality ofsituations, such as interoperatively and during patient trial. Moreover,trial stimulator system 100 (or portions thereof) is preferably adaptedfor use in providing stimulation to a plurality of tissues and/or areasof the body, such as spinal cord stimulation, deep brain stimulation,etcetera.

Trial stimulator system 100 of the illustrated embodiment includes trialstimulator 110, lead cable assembly 120, lead 130, and externalinterface platform 140. Although not shown in FIG. 1 for simplicity,trial stimulator system 100 may include one or more trial stimulatorholsters for holding and/or protecting trial stimulator 110, as will bediscussed in further detail below.

To facilitate user control thereof, trial stimulator 110 of theillustrated embodiment includes a user interface having keypads 111 and113, display 112, and audio (not shown) which may include a speaker foraudio output and/or a microphone for audio input. The user interface oftrial stimulator 110 preferably provides a plurality of user interfacemodes which appears and functions substantially the same as a userinterface of a pulse generator controller which will be used forcontrolling a pulse generator after the trial period. For example, afirst user interface of trial stimulator 110 may provide a spinal cordstimulation (SCS) patient interface which appears and functionssubstantially the same as a patient user interface of an implanted pulsegenerator (IPG) controller. A second user interface of trial stimulator110 may provide a SCS clinician interface which appears and functionssubstantially the same as a clinician user interface of an IPGcontroller. A third user interface of trial stimulator 110 may provide adeep brain stimulation patient interface which appears and functionssubstantially the same as a patient user interface of an IPG controllerwhile a fourth user interface of trial stimulator 110 provides a deepbrain stimulation clinician interface which appears and functionssubstantially the same as a clinician interface of an IPG controller.

Trial stimulator 110 couples to one or more lead cable assemblies 120,which in turn couple to one or more leads 130, to provide electronicstimulation pulses to electrodes 131. Lead 130 is inserted into apatient and positioned such that the end including electrodes 131 isdisposed near nerves or other tissue (e.g., muscle) for which electronicstimulation is desired. Lead 130 may comprise a trial lead (e.g., a leadwhich is not for permanent use, such as may be limited to use during atrial period of 30 days) or a permanent lead (e.g., a lead that is toremain implanted after conclusion of a trial period using trialstimulator 110. Where a permanent lead is used, an extension (not shown)may be coupled to the lead to externalize the lead and to provide asuitable interface to lead cable assembly 120.

The end of lead 130 including connectors 132 is inserted into quickconnect receiver 124 of lead cable 120 of the illustrated embodiment forelectrical connection of electrodes 131 to appropriate signal lines oflead cable 120. Lead cable 120 of the illustrated embodiment may becoupled to trial stimulator 110 at either of connectors 121 or 123. Forexample, connector 121 may be coupled to trial stimulator 110, withconnector 123 coupled to connector 122, to provide an extended leadcable as may be useful for clinician operation of trial stimulator 110during implantation of lead 130. However, connector 122 may be coupledto trial stimulator 110, with the portion of lead connector 130including connectors 121 and 122 removed, to provide a shortened leadcable as may be useful for patient trial operation of trial stimulator110.

Lead cable connectors, such as connectors 121 and 123, utilizedaccording to embodiments are preferably comprised of connectorconfigurations which securely lock into trial stimulator 110, and theoperation of which is readily understood by users thereof. For example,the illustrated embodiment employs a modular connector configurationcorresponding to that of an RJ45 8 pin connector, which are in widespread use for digital telephones and computer networks. The RJ45connector configuration includes a locking tab which providesappreciable locking capabilities as well as presenting a form factorwhich is familiar to a great number of users. Moreover, connectorsproduced according to an RJ45 connector configuration may be massproduced relatively inexpensively. However, although adopting an RJ45connector configuration, or other familiar form factor, preferredembodiments of the present invention do not utilize a connector which isdirectly interchangeable with a connector used for other, non-medical,systems. For example, an RJ45 connector configuration of embodiments mayinclude a key protrusion and/or detent in a surface thereof to preventthe lead cable from being inserted into an inappropriate interface, suchas a computer network interface, and/or to prevent an inappropriatecable, such as a computer network cable, from being inserted into thetrial stimulator.

Trial stimulator 110 of the illustrated embodiment includes a pluralityof multi-channel interfaces for coupling to one or more leads as shownin FIG. 2. Specifically, the illustrated embodiment includesmulti-channel interface 221 (shown in FIG. 2) as well as 3 additionalmulti-channel interfaces (not visible behind respective ones of flaps222). The multi-channel interfaces provide connectivity of multiplestimulation channels (e.g., channels 1-8, channels 9-16, channels 17-24,and channels 25-32 respectively) external to trial stimulator 110, suchas by mating with connector 121 of lead cable 120. When not in use, amulti-channel interface, such as multi-channel interface 221 may becovered by a corresponding one of flaps 222 for protection.

It should be appreciated that, although the illustrated embodiment oftrial stimulator 110 includes multi-channel interfaces accommodating 8channels and leads having 8 electrodes, embodiments of the invention mayprovide for any number of channels and electrodes. Likewise, there is nolimitation with respect to the use of 4 multi-channel interfaces orproviding 32 independent stimulation channels according to the presentinvention. For example, referring to FIG. 3, lead cable “Y” adapter 320is shown which facilitates coupling multiple leads, such as 2 leadshaving 4 electrodes each, to a single multi-channel interface, such amulti-channel interface 221. Embodiments of the invention may utilizeleads having fewer electrodes than the number of channels supported by atrial stimulator interface to which they are connected. For example,trial stimulator 110 may detect (or a clinician may indicate) that a 4electrode lead has been inserted into one or more of the multi-channelinterfaces, such as multi-channel interface 221.

FIG. 4 provides a high level functional block diagram of trialstimulator 110 according to an embodiment of the present invention.Trial stimulator 110 of FIG. 4 includes central processing unit (CPU)410, memory 420, input/output controller 430, external interface 440,interface control circuitry 450, and clock 480, all coupled by bus 400.Additionally, trial stimulator 110 of FIG. 4 includes multi-channelinterface 460 and stimulation power source 470 coupled through interfacecontrol circuitry 450. Accordingly, trial stimulator 110 of a preferredembodiment provides an integrated pulse generator and stimulation pulsecontrol system.

CPU 410 preferably operates under control of an instruction set andalgorithms, as may be stored in memory 420, defining operation asdescribed herein. In addition to storing the foregoing instruction setand algorithms, memory 420 may store operational data, such asstimulation parameters, stimulation programs, compliance monitorinformation, patient information, clinician information, historicalinformation, user help information, and/or the like.

Input/output controller 430 of the illustrated embodiment is coupled tokeypad 431, such as may correspond to keypads 111 and 113 of FIG. 1,display 432, such as may correspond to display 112 of FIG. 1, and audio433, such as may comprise an audio speaker and/or microphone, tofacilitate user control and interaction with trial stimulator 110.Accordingly, trial stimulator 110 may receive user input, such asthrough manipulation of keys of keypad 431 and/or by aural input throughaudio 433. Likewise, trial stimulator 110 may provide output to a user,such as by textual and graphical presentation on display 432 and/or byaural output through audio 433.

Display 432 is preferably configured to provide a relatively largedisplay area. According to a preferred embodiment, display 432 comprisesa 4 line by 20 character dot matrix liquid crystal display suitable fordisplaying text characters as well as bit mapped graphics. Display 432may be adapted to provide gray scale display, such as 4 or 8 bit grayscale, and/or may provide color display, such as 16 bit color, andpreferably includes a back light for easy viewing in many lightconditions.

External interface 440, such as may correspond to interface 114 of FIG.1, provides an external data connection for communication with devicesexternal to trial stimulator 110. For example, external interface 440may provide a bi-directional data link for interfacing an externalclinician user interface platform, such as may be provided by externalinterface platform 140 of FIG. 1.

External interface 440 may provide a wireline interface, such as maycomprise a serial interface (e.g., USB), a parallel interface, a localarea network (LAN) interface (e.g., Ethernet), a fiber optic interface,and/or the like. Additionally or alternatively, external interface 440may provide a wireless interface, such as may comprise a bluetoothinterface, an IEEE 802.11 interface, an IEEE 802.16 interface, acellular interface, a personal communications system (PCS) interface, aninfrared interface, and/or the like. Accordingly, external interface 440of embodiments of the present invention may provide for near field, farfield, and/or long distant remote interfacing with trial stimulator 110,such as to provide control, polling, programming, status monitoring,etcetera. It should be appreciated, therefore, that external interface440 of embodiments may provide connectivity to external devices inaddition to or in the alternative to the aforementioned externalinterface platform. For example, external interface 440 may be utilizedto provide connectivity to an external cathode ray tube (CRT), LCD flatpanel display, or other display device to accommodate larger or improveddisplay of user output. Similarly, external interface 440 may beutilized to provide connectivity to an external keyboard, digitizingtablet, digital pointer (e.g., mouse), or other input device toaccommodate larger or more complex user input. Likewise, externalinterface 440 may be coupled to a communication device, such as a modem,network interface card (NIC), and/or wireless access point, in order tofacilitate desired connectability with respect to trial stimulator 110.

Additionally or alternatively, external interface 440 may comprise anaccess port for reprogramming trial stimulator 110. For example, inaddition to providing an interface to an external platform such asexternal interface platform 140 of FIG. 1, external interface 440 maycomprise a hidden access port providing a proprietary interface forfacilitating software upgrades, low level diagnostics, core dumps,debugging, etcetera. According to one embodiment, external interface 440provides an access port from which instruction sets and algorithms ofmemory 420 may be reflashed.

Interface control circuitry 450 operates under control of CPU 410 toprovide stimulation pulses from stimulation power source 470 to selectedchannels of multi-channel interface 460, such as may comprise one ormore interfaces such as multi-channel interface 221 of FIG. 2. Forexample, stimulation power source 470 of a preferred embodiment maycomprise a battery and circuitry to function as a constant currentsource which may be selectively coupled to one or more independentstimulation channels of multi-channel interface 460 by interface controlcircuitry 450 to provide stimulation pulses of desired magnitude,frequency, pulse width, etcetera. Similarly, stimulation power source470 may be selectively coupled to stimulation channels of multi-channelinterface 460 by interface control circuitry 450 to provide an activedischarge pulse following a corresponding stimulation pulse.

Stimulation power source 470 preferably utilizes a commerciallyavailable battery, such as a 9 volt alkaline battery as is widelyavailable through retail outlets. Accordingly, a user of trialstimulator 110 may readily replace the battery of stimulation powersource 470 as needed. Additionally or alternatively stimulation powersource 470 may utilize a rechargeable battery to facilitate rechargingof the battery without replacement. However, such a rechargeable batteryconfiguration, without a replaceable battery, may necessitate carefuloperation of trial stimulator 110 to avoid depleting the battery duringa time or location that recharging is not practicable.

The battery of stimulation power source 470 provides energy foroperation of circuitry of trial stimulator 110 in addition to interfacecontrol circuitry 450 according to a preferred embodiment. For example,the aforementioned battery may provide power for operation of CPU 410,memory 420, input/output controller 430, external interface 440 and/orclock 480. Accordingly, backup power circuitry, such as may comprise acapacitor or rechargeable cell, may be provided to maintain energy toselect circuits for a minimum amount of time to facilitate a batterychange or recharge period. For example, backup power circuitry may beprovided with respect to memory 420 so that stimulation programs,stimulation parameter sets, historical information, etcetera is retainedduring a battery change, thereby providing a substantially non-volatilememory configuration.

Clock 480 preferably provides date and/or time information useful in theoperation of trial stimulator 110. For example, clock 480 may provide aclock by which the frequency of stimulation pulses provided by interfacecontrol circuitry 450 is controlled. Additionally or alternatively,clock 480 may provide real time information, such as a time of dayand/or a day of the week, for use in implementing different stimulationprograms, creating a historical database, monitoring compliance,instigating communications, etcetera.

As described above, stimulation power source 470 of a preferredembodiment provides a constant current source which may be selectivelycoupled to one or more independent stimulation channels of multi-channelinterface 460 by interface control circuitry 450 to provide stimulationpulses of desired magnitude, frequency, pulse width, etcetera.Accordingly, trial stimulator 110 of a preferred embodiment operates toprovide constant current stimulation pulses. For example, interfacecontrol circuitry 450 may switchably couple a properly configuredcurrent source circuit of stimulation power source 470 to an appropriatechannel of multi-channel interface 460 according to clock 480 andthereby provide constant current stimulation pulses having a desiredfrequency.

It should be appreciated that, if electrode impedances are identical, itdoes not matter whether a constant voltage pulse or a current pulse isprovided in achieving a desired level of stimulation. However, if theelectrode impedance changes over time, such as due to scar tissueforming around the electrodes, the lead shifting slightly due to patientmovement, etcetera, constant current stimulation is preferred overconstant voltage stimulation because it is the current between theelectrodes (the current density) that triggers the nerve to delivertherapeutic responses in neurostimulation. Accordingly, using a constantcurrent stimulation pulse according to embodiments of the presentinvention, a constant current field is provided around the electrodes,irrespective of what the impedance change is, thereby consistentlydelivering the desired stimulation response.

It might be argued that use of a constant current source in providingthe foregoing stimulation runs a risk of depleting the battery fasterand/or over stimulation (e.g., voltages appreciably in excess of thoseassociated with desired/prescribed currents with the expectedimpedance/load) in a situation where one or more electrodes becomeunexpectedly disconnected from the constant current source. For example,where a constant current source is configured to provide a desiredcurrent to 2 electrodes and 1 of those electrodes becomes disconnected(the impedance experienced by the system changes), the remainingelectrode may be provided with a voltage twice that desired. However, itshould be appreciated that the constant voltage configurations of priorart stimulators run a risk of over stimulation due to both voltage andcurrent being a part of Ohm's Law. In particular, if a constant voltagestimulator loses an electrode due to it becoming short circuited (i.e.,substantially zero voltage across the electrode), the impedance of thesystem would change resulting in an increased current being delivered toelectrodes and correspondingly an over stimulation situation (whereas,in a constant current system, the current would remain the same).

To address the foregoing risk of depleting the battery faster and/orover stimulation, preferred embodiments of interface control circuitry450 implement a constant current which is voltage limited. For example,CPU 410 may operate to determine an appropriate voltage limit (e.g.,maximum override voltage threshold) to establish with respect to aconstant current pulse which may be utilized by interface controlcircuitry 450 to allow provision of a desired current while preventingan over stimulation situation by establishing a maximum voltage for thestimulation pulse. By knowing the impedance or voltage at a currentsetting associated with an electrode, CPU 410 may select a voltage limitwhich allows some amount of voltage (e.g., a percentage, such as 10%) inexcess of that associated with delivering a prescribed current to thetissue to be stimulated while providing adequate over stimulationprotection. Such voltage limits are preferably determined automatically,such as upon a stimulation current level being selected or adjusted(e.g., a stimulation parameter set being adjusted), and may beestablished with respect to every stimulation pulse (including thepulses of a multi-stimulation program). This voltage limit informationmay be provided by CPU 410 to interface control circuitry 450 for use incontrolling signals to multi-channel interface 460.

Voltage limits for use with respect to each stimulation parameter setmay be determined according to embodiments using a voltage rampingtechnique. For example, when a stimulation parameter set is selected oradjusted, embodiments of the invention may operate to increase voltagelimit in small increments, making a compliance check to see if thevoltage is high enough to deliver the desired or prescribed constantcurrent pulse. If the desired or prescribed constant current pulse isnot delivered with a particular value of voltage limit, the voltagelimit may again be increased until a current compliance check error iseliminated. The voltage limit at that point (or perhaps some slightlyincreased value as discussed above) may be recorded for use with respectto the stimulation parameter set and the process repeated for each ofthe stimulation parameter sets within a multi-stimulation program.Therefore, a constant current system of embodiments of the presentinvention implementing a voltage limit will not over stimulate thepatient or deplete the battery more quickly. In contrast, the priorconstant voltage systems may over stimulate the patient and continuouscurrent systems without a voltage limit may deplete the battery morequickly.

Additionally or alternatively, impedance testing is provided by thecircuitry of trial stimulator 110 of preferred embodiments. For example,impedance testing may be utilized according to embodiments of theinvention in determining electrode impedances (e.g., determining theload to be driven by a constant current source), such as for use inautomatically establishing the foregoing voltage limits. Likewise,impedance testing may be utilized in providing a broken circuit detector(e.g., as may be implemented periodically, before each stimulationpulse, before particular stimulation pulses, etcetera), such as for usein alerting a patient or clinician that an electrode or electrodes arenot coupled to the trial stimulator and therefore stimulation pulses arenot being delivered thereto. A broken circuit detection circuit of apreferred embodiment provides an alarm or other alert to a user toprovide notification of the broken circuit and/or stops deliveringstimulation pulses, such as to avoid a patient or clinician increasingpulse magnitude before realizing a lead has become disconnected andthereby over stimulating the patient when the lead is subsequentlyreconnected. The aforementioned maximum voltage override of embodimentsof the invention may be utilized in providing a broken circuit detectionfeature. For example, when a maximum voltage override threshold for aparticular channel is reached, a trial stimulator operating program mayconclude that a circuit has been broken with respect to that channel.Such a maximum voltage override threshold may be used in combinationwith impedance data in determining a broken circuit condition accordingto embodiments of the invention. Impedance data may also be used to helpdetermine the proper location of the leads/electrodes, predict batterylife, help select implanted devices, etcetera.

Although some stimulation systems in the past have implemented a lightemitting diode (LED) to indicate when current was flowing to anelectrode or electrodes, such configurations provide no information withrespect to the impedance. Moreover, in order for the LED to beilluminated according to such configurations, an appreciable voltagelevel must be present, such as on the order of 1 Volt, thereby makingtheir use in determining electrode connectivity without providingstimulation which is perceptible to a patient substantially impossible.Such voltage levels may not be present in particular situations, such asdeep brain stimulation, without over stimulation, thereby making the LEDconfiguration ineffective in such situations.

According to an embodiment, interface control circuitry 450 operatesunder control of CPU 410 to provide impedance test signals by couplingcircuitry of stimulation power source 470 to channels of multi-channelinterface 460. In measuring impedance, interface control circuitry 450may cause low level pulses to be applied to the electrodes for whichimpedance testing is being performed. Preferably, the pulses are of alow magnitude, such as on the order of 50 to 100 microamps, and/or at arelatively high frequency, such as on the order of 50 kHz (e.g., 10microsecond pulse width), so that the impedance test signals do notprovide stimulation which is detected by the patient. In operationaccording to an embodiment, CPU 410 analyzes the voltage across the loadduring these impedance test signals to determine impedance.

According to a preferred embodiment, the impedance test signals areprovided as an alternating current (AC), substantially square wave,wherein an electrode is an anode during a first portion of the squarewave and a cathode during a second portion of the square wave.Accordingly, interface control circuitry 450 may switchably connectconstant current circuitry of stimulation power source 470 to theaforementioned electrode in a forward and reverse configuration toprovide high frequency impedance test signals without requiringsubstantial control of stimulation power source 470 to provide theaforementioned square wave. In this configuration, wherein a constantcurrent source is utilized, it should be appreciated that the voltageacross the load is proportional to the impedance. By applying theforegoing AC impedance test signal to electrodes for an appreciabletime, e.g., on the order of milliseconds, the differential voltages maybe averaged, perhaps using filtering, to provide impedance information.For example, the differential voltage change across the load may beconverted to a direct current (DC) value and provided to an analog todigital (A/D) converter for use in determining an impedance value by CPU410. In particular, the DC voltage will be linearly proportional toimpedance according to embodiments, thereby providing information usefulfor determining impedance.

The foregoing impedance testing technique implemented according topreferred embodiments provides a very low pulse width and very lowamplitude so that no perceptible stimulation will be delivered to apatient, including deep brain stimulation patients where the stimulationvalues are very low themselves. Moreover, filtering the differentialvoltages over a long period of time according to embodiments of theinvention provides for very accurate impedance determinations, such aswithin a few percent, and over a very large range, such as over a rangeof from 100 Ohms to 5 kOhms.

It should be appreciated that in the foregoing impedance testing may beutilized to provide an impedance value associated with an electrode orelectrodes. Moreover, the foregoing impedance testing may be utilized inproviding a broken circuit detector or other fault detector, such as byconcluding that a broken circuit is present with respect to an electrodewhen an impedance value is determined to be excessively high and/orconcluding that a short circuit is present with respect to an electrodewhen an impedance value is determined to be excessively low. Theforegoing information may be provided to a user, such as a patient orclinician, through output via a user interface of trial stimulator 110.

Embodiments of the present invention utilize impedance testing, such asusing the techniques described above, in providing system diagnostics.For example, upon power up, and/or at other appropriate times, trialstimulator 110 may operate to provide system diagnostics to verify theoperational status of aspects of system 100. Where a trial lead has beenplaced in a patient and a clinician is preparing to program trialstimulator 110 to provide stimulation, CPU 410 may first operate todetermine that the impedances associated with each electrode is withinexpected ranges, and thus that the electrodes are connected properly,that the lead is disposed properly, that the patient is a suitablecandidate for electrostimulation therapy, etcetera.

According to a preferred embodiment, CPU 410 controls interface controlcircuitry 450 to couple stimulation power source 470 to channels ofmulti-channel interface 460, and thus the corresponding electrodes.Specifically, electrodes may be energized in bipole pairs (cathode andanode), “walking” the test signals from bipole pair to bipole pair toobtain impedance information for each electrode and thereby test all theconnections. For example, in determining system integrity a diagnosticalgorithm may provide a test signal to channels 1 and 2 (correspondingto electrodes 1 and 2) wherein the electrodes are energized as bipoles(plus/minus), wherein this bipole energization is repeated for the otherelectrodes in bipole pairs (electrodes 2 and 3, electrodes 3 and 4,etcetera). By measuring the impedance in each such step, conclusions maybe made with respect to each channel and associated electrode. Forexample, if an open circuit is detected with respect to channels 1 and 2(electrodes 1 and 2), testing of channels 2 and 3 (electrodes 2 and 3)should provide information as to whether channel 1 (electrode 1) orchannel 2 (electrode 2) is the source of the open circuit.

CPU 410 may provide conclusions based upon impedances associated with anelectrode being within an expected range (e.g., 200-3000 Ohms), too low,or too high. For example, if an impedance associated with an electrodeis not within an expected range, a user interface of trial stimulator110 may provide a warning to the user, e.g., a clinician, and/or makesuggestions with respect to correcting the problem, e.g., suggestingthat the connections be checked, suggesting that the position of thelead be verified, etcetera.

Embodiments of the present invention are adapted to provide activedischarge which respect to stimulation pulses in order to facilitatehigh pulse rate (high frequency) operation. For example, trialstimulator 110 of a preferred embodiment may be utilized to providestimulation pulse frequencies anywhere in the range of from 2 Hz to 1200Hz. However, the impedances associated with electrodes implanted inliving tissue may be relatively high, such as on the order of 1500 Ohms.In providing stimulation to the electrodes, DC current is preferablyblocked to prevent tissue damage, such as may result fromelectroplating. Accordingly, interface control circuitry 450 and/ormulti-channel interface 460 of preferred embodiments include DC blockingcapacitors with respect to each channel so that there is no net DCassociated with the stimulation pulses. Accordingly, it should beappreciated that there will be a resistor/capacitor (RC) time constantassociated with the stimulation circuit according to embodiments. ThisRC time constant may be appreciably large because the pulses may be onthe order of milliamps and the resistance may be relatively large.

Directing attention to FIG. 5A, a graph of a stimulation signalassociated with passive discharging of the foregoing RC circuit isshown. In particular, passive discharge curve 501 represents theforegoing RC time constant, which if not allowed to reach a transientstate will affect the subsequent stimulation pulse shape. From FIG. 5Ait can be seen that passive discharging of the RC circuit may provideacceptable results when stimulation pulses are spaced apart sufficientlyin time (e.g., low frequency stimulation, such as 250 Hz or below).However, as stimulation pulses are moved closer and closer together intime, passive discharge curve 501 will not be allowed to return to atransient state and, thus, subsequent stimulation pulses will beaffected.

Embodiments of trial stimulator 110 provide for high frequencystimulation pulses. In particular, trial stimulator 110 of a preferredembodiment provides for multi-stimulation programs wherein stimulationparameter sets of multiple stimulation programs are interleaved on apulse-by-pulse basis. Even where a particular stimulation programprovides for stimulation pulses with a frequency of 100 Hz (a relativelylow frequency stimulation program), a multi-stimulation program wherein8 such stimulation programs are interleaved on a pulse-by-pulse basisresults in a stimulation pulse frequency of 800 Hz (a relatively highstimulation pulse frequency).

Active discharge is implemented according to embodiments of the presentinvention to facilitate high frequency stimulation pulses. In providingactive discharge according to embodiments, interface control circuitry450 couples stimulation power source 470 to channels of multi-channelinterface 460 such that current is driven in a first direction for aperiod of time, thereby providing a stimulation pulse, and then drivenin a second, or reverse, direction for a period of time, therebyproviding a discharge pulse. FIGS. 5B and 5C show graphs of stimulationsignals associated with active discharging of the foregoing RC circuit.In particular, active discharge pulses 502 and 503 (of FIGS. 5B and 5Crespectively) actively discharge the RC circuit, facilitating placingstimulation pulses closer together in time.

In order to provide complete discharge of the RC circuit, the energy ofthe discharge pulse (the area of the discharge pulse curves as shown inFIGS. 5B and 5C) is preferably equal to the energy of the proceedingstimulation pulse (the area of the stimulation pulse curves as shown inFIGS. 5B and 5C). However, as can be seen by discharge pulses 502 and503, the pulse width and amplitude of the discharge pulses need not bethe same as the pulse width and amplitude of the stimulation pulse. Itshould be appreciated that constant current stimulation implementedaccording to embodiments of the present invention simplifiesimplementation of active discharge as described above due to the pulseamplitudes (current) being known and constant.

According to a preferred embodiment, the amplitude of a discharge pulseis substantially minimized in order to avoid its being perceived by thepatient, or otherwise impacting the therapeutic effects of thestimulation pulse. Accordingly, where stimulation pulse frequency islower, the pulse width of the discharge pulse may be lengthened (andcorrespondingly the amplitude of the discharge pulse may be decreased)as shown in FIG. 5C. However, as stimulation pulse frequency isincreased, the pulse width of the discharge pulse may be shortened (andcorrespondingly the amplitude of the discharge pulse may be increased)as shown in FIG. 5B to facilitate stimulation pulses more closely spacedin time.

The foregoing active discharge is implemented selectively, according toembodiments of the invention. For example, CPU 410 may operate toimplement active discharge when the frequency of energizing pulsesexceeds a threshold, such as 200 Hz. Accordingly, where a stimulationprogram or multi-stimulation program provides stimulation pulses at afrequency of 200 Hz or below, passive discharge as shown in FIG. 5A maybe used. CPU 410 of the illustrated embodiment may selectively implementdifferent active discharge modes. For example, a 1 to 4 energizing pulseto discharge driving pulse mode as illustrated in FIG. 5C may beimplemented with respect to a first frequency range, such as 200 Hz to500 Hz, and a 1 to 2 energizing pulse to discharge driving pulse mode asillustrated in FIG. 5B may be implemented with respect to a secondfrequency range, such as 500 Hz to 1000 Hz.

External interface platform 140, as may be used to interface with and/orcontrol trial stimulator 110, may comprise any number of processor-basedsystems which provide suitable input/output for providing a userinterface as described herein and for interfacing with trial stimulator110. For example, external interface platform 140 of embodiments of thepresent invention comprise a personal digital assistant (PDA), such as apocket PC operable under control of the WINDOWS CE operating system, asare well known in the art. A PDA may provide a particularly desirableexternal interface platform because of their portability, their wideavailability, their relatively versatile display and user inputcharacteristics, their ability to be interfaced using a variety of media(whether wireless or wireline) and protocols, and their ability to beconfigured to provide dedicated operation (i.e., to the exclusion ofother application programs) as an external interface according to thepresent invention. Accordingly, external interface platform 140comprises a PDA operable under control of an instruction set definingoperation as described herein, according to embodiments of the presentinvention. Of course, external interface platform 140 may comprise aprocessor-based system other than the aforementioned PDA. For example,external interface platform 140 of embodiments of the present inventioncomprises a general purpose portable computer system, such as a notebookcomputer operable under control of a WINDOWS, LINUX, MAC OS, UNIX, oroperating system, and having an instruction set defining operation asdescribed herein. According to alternative embodiments of the invention,external interface platform 140 comprises a special purpose device, suchas may include application specific integrated circuits (ASICs),firmware, etcetera, adapted to provide operation as described herein.

Having described trial stimulator 110, lead cable assembly 120, lead130, and external interface platform 140, of embodiments of the presentinvention, operation of trial stimulator system 100 in providing trialstimulation according to embodiments of the invention shall bedescribed. Trial stimulator system 100 of embodiments of the presentinvention may be used in providing stimulation to a plurality of tissuesand/or areas of the body, such as spinal cord stimulation, deep brainstimulation, peripheral nerve stimulation, vagas nerve stimulation,gastric stimulation, occipital nerve stimulation, sacral root nervestimulation, etcetera. Accordingly, a user interface provided by trialstimulator 110 and/or external interface platform 140 providesmulti-mode patient and/or clinician interfaces adapted to present aninterface specific to a particular use. For example, although perhapssharing a number of features and functions, separate patient and/orclinician interfaces for spinal cord stimulation and deep brainstimulation may be provided with respect to trial stimulator 110 andexternal interface platform 140. Utilization of a particular mode mayprovide for different trial stimulator operating characteristics, suchas to implement smaller or larger amplitude increments when adjusting astimulation pulse amplitude parameter in the various modes of operation.

Trial stimulator system 100 is adapted for use in a plurality ofsituations, including interoperative use and patient trial use.Accordingly, trial stimulator 110 of a preferred embodiment provides auser interface which is adapted for patient trial use. For example,trial stimulator 110 may provide an intuitive interface havinggraphical, textual, and/or aural prompting and simple user input.According to one embodiment, graphical displays such as may include abattery life indicator, stimulation pulse amplitude and/or frequency,etcetera are provided to aid a user in readily interpreting the statusof various aspects of a trial stimulator. Trial stimulator 110 of apreferred embodiment provides a patient interface which appears andfunctions substantially the same as a user interface of a pulsegenerator controller which will be used for controlling a pulsegenerator (implanted or otherwise) after the trial period, therebyallowing a patient to learn a single interface.

Embodiments of trial stimulator 110 additionally or alternativelyprovide a user interface which is adapted for clinician use. Forexample, a trial stimulator user interface configured according toembodiments of the invention may facilitate simplified use between aplurality of patients by automatically resetting stimulation parametersets and/or other parameters to an initialization state (or perhapsquerying a clinician in this regard) when a clinician mode is entered. Aclinician user interface of trial stimulator 110 may provide additionalfeatures, such as a compliance monitor, system diagnostic options,etcetera. For example, a compliance monitor may record information withrespect to the operation of a trial stimulator, including stimulationparameters, programs implemented, time and duration of operation ofstimulation sets, etcetera, in order to allow a clinician tosubsequently determine if a patient has used the trial stimulatoraccording to a prescribed therapy, to diagnose a patient's reportedindications, etcetera. Diagnostic options may facilitate a clinicianverifying proper operation of various aspects of a trial stimulator,such as to implement the above described impedance testing techniques.Although such diagnostics may be implemented automatically, such as onpower up or upon entering a programming mode, the clinician userinterface may provide the results of such diagnostics to the user.Moreover, such diagnostic routines may be implemented under control of auser, via the aforementioned user interface, such as to facilitatetesting of a lead and its electrodes when a pulse generator is beingreplaced at the end of its battery life. Such diagnostics may allow aclinician to avoid the unnecessary replacement of a lead during theprocedure.

Full clinician user interface functionality, such as may includeinitialization, programming, monitoring, status reporting, etcetera, ispreferably included within trial stimulator 110. For example, aclinician interface incorporated within trial stimulator 110 of anembodiment may provide an interface which appears and functionssubstantially the same as a clinician interface of a pulse generatorcontroller which will be used for controlling a pulse generator(implanted or otherwise) after the trial period, thereby allowing aclinician to learn a single interface.

In use, a clinician may insert lead 130 into a patient for whichneurostimulation trial using trial stimulator 110 is desired. Lead 130may be coupled to trial stimulator 110 via lead cable assembly 120.According to embodiments of the invention, trial stimulator 110 mayremain outside of a sterile field associated with the patient byemploying an extension cable portion of lead cable assembly which endsat connector 122 and connector 121. In particular, lead cable assembly120 having the aforementioned extension cable portion included therewithprovides a lead cable which is relatively long, such as on the order of6 feet, to facilitate its being run beyond the drapes of a surgicalsterile field.

Once coupled to lead 130, a clinician may utilize keypads 111 and 113,display 112, and/or audio (not shown) of trial stimulator 110 to performvarious functions, such as power up, diagnostics, patientinitialization, stimulation parameter set programming, multi-stimulationprogramming, etcetera. Of course, one or more of the foregoing may beperformed without trial stimulator 110 being coupled to lead 130, ifdesired.

In operation according to a preferred embodiment, upon power up of trialstimulator 110 and/or when coupled to lead 130, when entering aclinician mode, diagnostic routines are preferably entered to provideimpedance testing of the channels and associated electrodes.Accordingly, connection information, and perhaps alarms, may be providedto a clinician or other user. Such information is particularly useful inproviding programming of trial stimulator 110 because a connectionbetween trial stimulator 110 and one or more of electrodes 131 may bemissed, such as by misalignment of contacts 132 in quick connectassembly 124, resulting in a clinician believing that a patient is beingstimulated when in fact the patent is not. With the foregoing impedancecheck, it can be confirmed that the stimulation pulses are in factmaking it into the patient's body. Additionally or alternatively, theforegoing impedance information may be utilized to determine if thepatient is a good candidate for electrostimulation, such as where theelectrodes are disposed in a particularly high impedance spot making thepatient poorly suited for electrostimulation using an implantablegenerator (although perhaps a RF generator having a larger batterycapacity may still provide suitable operation).

Additionally or alternatively, entry of a clinician mode trialstimulator 110 queries the clinician as to whether a new patient istrialing the stimulator so as to facilitate simplified resettingparameters as well as to ensure that a previous patient's stimulationprograms are not accidentally implemented with respect to a subsequentpatient.

In clinician mode, a clinician may set/adjust the parameters of astimulation program or programs. For example, a clinician may setamplitude, pulse width, frequency, and electrodes to create one or morestimulation parameter sets of a stimulation program or multi-stimulationprogram.

A clinician interface of trial stimulator 110 may provide for selectionof amplitude with respect to any electrode through programming aconstant current source. According to a preferred embodiment, multipleranges of amplitude are selectable, each of which provides multiple bitsof amplitude resolution. For example, three amplitude ranges, such asfrom 0 to 6.125 milliamps, from 0 to 12.25 milliamps, and from 0 to 25.5milliamps. According to an embodiment, each amplitude provides 256 bitsof resolution. Accordingly, the 6.125 milliamp range provides forincrements of 0.025 milliamps, the 12.25 milliamp range provides forincrements of 0.05 milliamps, and the 25.5 milliamp range provides forincrements of 0.1 milliamps. Selection of the appropriate amplituderange and step size may be made by selecting the indication the trialstimulator is being used for. For example, selecting “deep brainstimulation” may select the 0 to 12.25 milliamp range and provide for0.05 milliamp adjustment increment steps, while selecting “spinal cordstimulation” may select the 0 to 25.5 milliamp range and provide for 0.1milliamp adjustment increment steps.

Pulse width with respect to any electrode as selectable through aclinician interface of trial stimulator 110 of an embodiment may providea range of pulse widths from 20 microseconds to 500 microseconds,although alternative embodiments provide for pulse widths in the rangeof 10 microseconds to 1000 microseconds. The ranges of pulse widths madeavailable according to embodiments of the invention may be adjustedbased upon the particular type of stimulation being implemented, e.g.,spinal cord stimulation, deep brain stimulation, etcetera. Trialstimulator 110 of an embodiment provides pulse width selectionresolution of 10 microsecond, although other pulse width resolutions maybe implemented according to the concepts of the invention.

Frequency with respect to any electrode as selectable through aclinician interface of trial stimulator 110 of an embodiment may providea range of frequencies from 2 to 1200 Hz. According to embodiments ofthe invention, frequency selection step sizes provided by a clinicianinterface are adjusted to correspond to a frequency range of thestimulation pulse. For example, when a stimulation pulse frequency islow, frequency selection step sizes may be small, e.g., 2 Hz, whereaswhen a stimulation pulse frequency is higher, frequency selection stepsizes may be larger, e.g., 10 Hz, and so on. According to a preferredembodiment, frequency step sizes go from 2 to 250 Hz in 2 Hz steps, from250 to 500 Hz in 5 Hz steps, and from 500 to 1200 Hz in 10 Hz steps.

Embodiments of trial stimulator 110 implement active discharge asdescribed above when stimulation pulse frequencies exceed a threshold.For example, when a stimulation frequency, whether associated with asingle stimulation program or a multi-stimulation program, exceeds 250Hz, active discharge is implemented.

The foregoing clinician functions, as well as additional clinicianfunctions well known in the art, are preferably provided by a clinicianinterface of trial stimulator 110 in a format corresponding to aclinician interface of a pulse generator expected to be used long termby the patient. Accordingly, a clinician may be enabled to use theforegoing interface without substantial or additional training. However,in order to facilitate an intuitive patient interface and full featuredand intuitive clinician interface without presenting a number of inputsand/or outputs which, although present in a patient trial mode, are notused by a patient, embodiments of the present invention implement anexternal clinician interface as provided by external interface platform140.

According to embodiments of the invention, external interface platform140 couples to trial stimulator 110 and allows the clinician to takecontrol of trial stimulator 110 using external interface platform 140.Accordingly, although a clinician may be enabled to access all featuresand functions through manipulation of an interface integral with trialstimulator 110, a more robust interface, perhaps using enhancedgraphics, color, sound, speech recognition, etcetera, may be provided toa clinician using external interface platform 140.

External interface platform 140 of a preferred embodiment operates undercontrol of trial stimulation software to define operation as describedherein. For example, menus may be presented to access various functionsas described above with respect to a clinician interface of trialstimulator 110. However, external interface platform 140 preferablyutilizes resources thereof to provide enhanced input/output. Forexample, in implementing the aforementioned diagnostic modes, externalinterface platform 140 may present the impedance ranges of eachelectrode in graphical form, or some other easily understood format.Moreover, additional processing may be provided by external interfaceplatform 140, such as to place information in spreadsheets, to compilegraphs, to analyze data, keep patient records, etcetera.

Additionally or alternatively, external interface platform 140 ofembodiments may provide processing to supplement or replace that oftrial stimulator 110 when coupled thereto. For example, theaforementioned techniques for determining impedances of electrodes maybe sufficiently processor intensive to require appreciable time incompleting diagnostics by trial stimulator 110. Accordingly, whencoupled to external interface platform 140 the processing power of theexternal interface platform may be utilized to complete such diagnosticprocessing more rapidly.

A holster or housing is preferably provided for use by a clinician whenexternal interface platform 140 is coupled to trial stimulator 110. Forexample, a piggyback holster arrangement, wherein a single holsterassembly holds both trial stimulator and external interface platform 140in a back-to-back configuration facilitates the holding together of theforegoing devices for simplified use in the operating room. Preferably,such a piggyback holster provides protection of trial stimulator 110,such as to cover one or more key pad buttons, display, interface ports,etcetera for which access is not needed during programming or cliniciantrial. However, interfaces such as interface 221 and 114 are preferablyunobstructed by the aforementioned piggyback holster configuration tofacilitate coupling of trial stimulator 110 to lead cable assembly 120and to external interface platform 140. Additionally, a preferredembodiment of a piggyback holster provides a gap to facilitate wrappingof excess cable, e.g., excess portions of lead cable assembly 120,around the holster while trial stimulator 110 and external interfaceplatform 140 are in use.

After having been programmed by a clinician, trial stimulator 110 ispreferably made available for trial by a patient. Accordingly, whereexternal interface platform 140 has been used in programming, externalinterface platform 140 is preferably uncoupled from trial stimulator110. Likewise, the aforementioned piggyback holster may also be removed.Because the patient is unlikely to need the length of lead cable used bya clinician, an extension portion of lead cable assembly 120 may beremoved such that connector 123 is directly interfaced with trialstimulator 110. Accordingly, a patient need not deal with an excessiveamount of lead cable being coiled during a patient trial according toembodiments of the invention.

A holster or other housing is preferably provided to facilitate apatient's trial of the stimulator. For example, a protective holsterhaving a clip which rotates 180 degrees may be provided to hold trialstimulator 110 on an article of clothing for patient access. The holstermay provide a keypad cover to protect accidental keypad presses,preferably leaving particular keys available, such as stimulation off,increase/decrease stimulation amplitude, or other keys typicallyaccessed in normal use.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the invention asdefined by the appended claims. Moreover, the scope of the presentapplication is not intended to be limited to the particular embodimentsof the process, machine, manufacture, composition of matter, means,methods and steps described in the specification. As one will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized. Accordingly, the appended claims areintended to include within their scope such processes, machines,manufacture, compositions of matter, means, methods, or steps.

1-9. (canceled)
 10. A trial stimulator system comprising: a processorfor controlling the trial stimulation system under control of executableinstructions, the instructions defining: (i) a patient user interfaceproviding user control during a patient stimulation trial; and (ii) aclinician user interface providing user control during a clinicianstimulation trial; and stimulation source circuitry comprising: (i)circuitry for providing constant current for output for stimulation of apatient; and (ii) a maximum voltage override circuit, coupled to thecircuitry for providing, to prevent delivery of current to the patientthat would cause an output voltage to exceed a maximum voltage value,wherein the processor controls the stimulation source circuitry toprovide stimulation according to a multi-stimulation set program thatdefines multiple pulses to be interleaved, each set of themulti-stimulation set program defining independent pulse parametersincluding an amplitude parameter, wherein the maximum voltage overridecircuit is controlled by the processor to apply an independent maximumvoltage value for each set of the multi-stimulation set program; whereinthe processor is operable to control the stimulation source circuitry toselectively provide active discharge of capacitors for stimulationfrequencies above a threshold frequency and to vary pulse widths ofdischarge pulses for stimulation frequencies above the thresholdfrequency.
 11. The system of claim 10, wherein said patient userinterface emulates a patient user interface of a first externalcontroller of a stimulation signal generator to be used after saidpatient stimulation trial, and wherein said clinician user interfaceemulates a clinician user interface of a second external controller ofsaid stimulation signal generator to be used after said patientstimulation trial.
 12. The system of claim 10, further comprising: anexternal clinician user interface platform interface to provide datacommunication with an external clinician user interface platform,wherein when said external clinician user interface platform is in datacommunication with said external clinician user interface platforminterface, the clinician user interface on the trial stimular system isactivated.
 13. The system of claim 10, wherein the instructions furtherdefine: a compliance monitor providing monitoring of operation of saidsystem for detection of use other in accordance with a prescribedtherapy.
 14. The system of claim 10, wherein the instructions furtherdefine: an impedance testing circuit operable in cooperation with saidstimulation source circuitry to provide impedance information associatedwith electrodes coupled to said system.
 15. The system of claim 10,further comprising: memory storing a plurality of multi-stimulation setprograms. 16-23. (canceled)